The present invention relates to a safety device for a throttle of an internal combustion engine and, more particularly, pertains to a new and improved safety device for a throttle of an internal combustion engine wherein the engine, such as a small two-cycle gasoline engine, includes an electric ignition device especially adapted for portable working machines, such as a hedge trimmer, an edger and the like.
Generally, a throttle of such kind for controlling an opening of a throttle valve of the internal combustion engine, a power source of the portable operation machines, comprises a throttle trigger (throttle lever) mounted on a handle or an operation rod, wherein an operator grips, one-handed, a hand grip portion of the handle, or the operation rod, while operating the throttle trigger with fingers of the gripping hand, so that the opening of the throttle valve can be adjusted to control engine power.
In such a throttle of the internal combustion engine, adapted for hedge trimmer and the like, when the operator releases the throttle lever to have the engine idle, a centrifugal clutch is automatically disconnected and operation of blade member is suspended. However, in case where unforeseen accidents arise, such as malfunction of the throttle in mowing operation and the like due to intrusion of grass or dust into the internal combustion engine, the engine speed cannot be decreased, even though the throttle lever has been released by the operator, and the blade member continues to rotate, which, in turn, could cause an irreparable accident. Otherwise, if some portions of the operator's body inadvertently contact with the throttle lever, the engine speed would quickly increase and cause a dangerous situation.
Assignee of the present invention has proposed a throttle device for an internal combustion engine, as disclosed in Japanese Unexamined Patent Publication No. Hei 2-163427, wherein a lock of the throttle lever is released only when the operator grips a safety lock lever, attached to the handle, as well as the throttle lever.
Other references, such as Japanese Examined Utility Model Publication No. Sho 56-32574, have suggested that a safety mechanism for an operation device of an internal combustion engine, adapted for a portable trimmer wherein the mechanism includes a stop switch, for automatically bringing the engine to a stop, in a manner that a movable contact, attached to the throttle lever, gets in contact with a fixed contact, attached to a body, when the operator releases the throttle lever, in operation of the trimmer.
In the former prior art, as described above, because the throttle lever can be mechanically looked, interconnecting with the safety lock lever, quick increase of the engine speed, due to inadvertent contact of some portions of the operator's body with the throttle lever and the like, can be prevented and dangerous situation can be avoided. However, this kind of prior art has a safety problem in that, because such a device cannot completely stop the operation of the engine, in case of the foregoing unforeseen malfunction of the throttle, the engine speed cannot be decreased, even though the throttle lever has been released by the operator, and the blade member continues to rotate, which, in turn, would cause an irreparable accident.
On the other hand, in the foregoing latter prior art, because the safety mechanism is constructed as electrically interconnecting the terminals, this kind of prior art has a reliability problem, as a safety device, in that such troubles, as a breaking of wire or a short circuit, could cause unexpected accident.